fix wrong tense
update perlexperiment

- fixed a typo (%H instead of %^H)
- removed mention of Unicode support, which is so deep that I doubt that
  it could ever be removed
- added the following items to the "Current experiments" section
  - alloccopstash
  - cop_store_label
  - gv_fetchmethod_*_flags
  - op_scope
  - op_lvalue
  - Smart match (~~)
  - Lexical $_
  - Array and hash container functions accept references
  - Regular Expression Set Operations

- moved the following items to the "Accepted features" section
  - fork() emulation
  - Weak references
  - Internal file glob
  - 64-bit support
  - die accepts a reference
  - DB module

- moved the following items to the "Removed features" section
  - GetOpt::Long Options
  - 5.005-style threading
  - Test::Harness::Straps
  - perlcc
  - Assertions
  - The pseudo-hash data type

I tried to add the corresponding Perl versions of when features were added
and accepted or removed, but used the stable versions as I searched in the
perldelta's.
final version and perlhist update for 5.18.0